Ask the Expert Question-and-Answer Archive

by Ron Joseph

August, 2003

Air Changes in Spray Booth

Q. We are designing a new paint booth in our company. I want to know about the minimum air changes required in a paint booth. How do I do the static pressure calculation?

A. Spray booths don't require air changes, such as bathrooms, kitchens, etc.. Instead, you need to follow the guidance of National Fire Protection Association Bulletin NFPA-33. You can download this from the Internet at www.nfpa.org, but there is a small charge.

Basically, you should insure that at no time do you exceed 25% of the Lower Flammable Limit (LFL). As a rule of thumb, the old guidance was that you should have at least 100 ft/min of air passing the face of the painter. Remember, you do not only want to extract the vapors, but you also want to carry the overspray (paint particulates) to the filters. If you meet the 25% LFL requirement but don't have sufficient airflow, the paint particulates will simply fall onto the floor of the spray booth

If you know the cross sectional area of the spray booth in the direction of airflow, you can calculate the volume of air (cf.) that must be extracted.